Simulator for continuous frequency modulated sonar

ABSTRACT

A multi-band-pass filter circuit with sequential detectorsampling means utilizing an azimuth function generator, programmable oscillator, lost time function generator means, range time base and range attenuator filter means together with a cathode-ray tube display (CRT) means and audio equipment for simulating realistically on the CRT and in the audio spectrum sonar echo signals representative of variations of target range, azimuth, conditions of relative movement, and including the effects of reverberation, lost time, and ambient, own ship and target noise conditions.

tates aterat SIMULATQR FOR CGNTHNUOUS FREQUENCY MQDULATED SUNAR 5] Feb.35,1972

OTHER PUBLICATIONS Damon, M. H., Jr., Electronics, Mar. 25. [960, "Tape72 inventor: Francis J. Murphree, Winter Park, Fla. Target Classifier Trm Sonar Operators? p [73] Assignee: The United States of America as 'rExamiltler Rodney Bennett represented by the Secretary off the NavyAmman f Momma A!turney-R|chard S. Scrascra and John W, Peasc [22] Filed:May 11, 1970 [21] Appl. No.: 36,237 ABSTRACT A multi-band-pass filtercircuit with sequential detector-sam- 52 piing means utilizing anazimuth function generator, pro- [51] grammable oscillator, lost timefunction generator means, [58] range time base and range attenuatorfilter means together with a cathode-ray tube display (CRT) means andaudio [56] Reierences Cited equipment for simulating realistically onthe CRT and in the audio spectrum sonar echo signals representative ofvariations FOREIGN PATENTS OR APPLICATIONS of target range, azimuth,conditions of relative movement, and 929,487 6/ i963 Great Britain ..35/10.4 including the effects of reverberation, lost time, and ambie ownship and target noise conditions 5 Claims, 6 Drawing Figures Ami E7 7MA}? flaw/ 56 M/Qf 6 V v #4 /22 Pa #5 Z load 7 U4 5 feverfiemfiohzzy/75in llama/4'17 jfimmw s ewer lfenem far e/won Aflmaa 72k l e/war /ZA? a a w 4 34 i L 44 z I d Programmed 7 -7 5 m 1 at; fl ya, 7

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sum 2 0F 5 SIMULATOR FOR CONTINUOUS FREQUENCY MODULATED SONAR STATEMENTOF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION Training in the use of CTFM sonars has beenaccomplished in the past by operation of actual field equipment or byuse of recordings made during such operation which are played backthrough a similar system at some later time. The use of actual equipmentis costly while the use of recordings lacks flexibility for variation ofconditions.

The object of the subject invention is to provide means for simulatingthe performance of a CTFM sonar to the extent that the simulated signalsounds realistic and appears realistic on a cathode-ray tube (CRT) andwhich is at the same time variable at will for the introduction ofselected variable problems.

SUMMARY OF THE INVENTION A simulator having a CRT display and audiosystem wherein problem variation signals, reverberation, ambient noise,own

ship noise and target noise are introduced to a system including anazimuth function generator, programmable oscillator, azimuth attenuatormeans and summing networks for application to a plurality of band-passfilter circuits, the outputs being applied to an audio system andthrough detectors and a detector sequential sampler to the CRT displayand wherein signals from a range time base source is used in conjunctionwith a lost time function generator and lost time gate means to producein the audio system and on the CRT a realistic simulation of the loss ofsignal between sequences of transmitted signal.

DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of a continuoustransmission frequency modulated (CTFM) sonar simulator embodying theinvention;

FIG. 2 is a graph of frequency and time relation between transmitted andmaximum range received signals for a CTFM sonar provided to betterunderstand the lost time signal factor;

FIG. 3 is a schematic drawing of one suitable lost time functiongenerator shown in block in FIG. 1;

FIG. 4 is a set of time curves constituting a timing diagram for thelost time generator function;

FIG. 5 is a block diagram of one suitable azimuth function generator;and

FIG. 6 is a block diagram of a suitable azimuth attenuator.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawing, the simulator shown therein provides the function ofintroducing problem variables to a computer 10 which provides an azimuthcommand signal on line 12 to an azimuth function generator 14 and arange command signal on a line 16 to a programmable oscillator 18. Theazimuth function generator provides on a line 20 the horizontal scaninput to a cathode-ray tube display (CRT) 22. The azimuth functiongenerator also provides one input on lines 24 and 25 to a first azimuthattenuator 26. The second input to the azimuth attenuator 26 is providedon a line 28 from the oscillator 18 via a line 33 and gate 29. Gate 29receives an input from the azimuth function generator 14 via lines 24.3i and 27. The output from azimuth attenuator 26 is passed on lines 30,32 and 34 and 36 via a gain control 38 and a first summing network 40 toa plurality of band-pass filter channels, each including a band-passfilter and associated detector identified hereinafter. The drawing forsimplicity is limited to two channels constituting a band-pass filter 42and associated detector 44 connected by a line 46 and a band-pass filter48 and detector 50 connected by a line 52. In an actual simulator some30 or more band-pass filter channels may be employed. The output ofdetectors 44 and 50 are passed on lines 54 and 56 to a detector sampler58 for sequentially sampling the band-pass channel detectors 44 and 50.One output of the detector sampler 58 is passed on line 60 to provide avertical scan input to the CRT 22. A second output from the detectorsampler 58 via lines 62, 64 and a gain 66 provide the intensity ofbrightness input to the CRT 22. The portion of the circuit of FIG. 1thus far described relates to the introduction of signals responsive torange and azimuth commands.

However, a realistic simulation of actual CTFM sonar requires theintroduction of lost time function. As shown in FIG. 2, this is theperiod of loss of signal between repeated transmissions. Lost time" iscaused by the fact that immediately after the modulated sawtoothtransmitted signal ceases its transmission signal and returns to itsstarting point for the next signal, the difference between the frequencybeing transmitted and that being returned from the target or scatterer,indicated as F is too great to pass through the receiver filters. Losttime" lasts for 2R/C seconds, i.e., the time required for the sound topropagate to a range R and to return. For example, if a hydrophone (notshown) is pointed at a target (not shown) 800 yards distant from whichan echo is being received, at the instant the sawtooth transmissionsignal returns to its retransmission starting point the echo wouldapparently cease for 1 second. Nearer targets would cease for shorterintervals. The echo would then be heard until flyback again occurred andthe cycle repeated.

To simulate this phenomena, lost time" gates 68 and 70 (see FIG. I) areprovided for the respective band-pass channels shown in FIG. 1 receivinginputs from respective lines 34 and 36 and inputs on lines 71 and 72from a "lost time function generator 74 which receives its input on line76 from a time base pulse source 78 identified as a range time basewhich provides one cycle of transmission when the transmitted signalbegins and one cycle of transmission when the transmitted signal ends.Outputs from the respective lost time" gates 68 and 70 are passedrespectively via line 80, summing network 82 and line 84 to band-passfilter 42 and via line 86, summing network 88 and line 90 to band-passfilter 48. The summing networks 40, 82 and 88 are provided because ofadditional phenomena of reverberation and noise as will be presentlydescribed hereinafter.

Realistic simulation also requires. simulation of reverberation causedby sound scattered from bottom, surface and volume of the water whichmay be heard from all ranges and bearings and would show on the CRT.Simulation is also required for ambient, own ship and target noiseswhich may also be present.

To simulate reverberation, I provide a reverberation generator 94connected via line 98, gain control and line 102 as one input to a rangeattenuation filter 96. The second input to the range attenuation filteris obtained from the range time base 78 via a line 104, The output ofthe range attenuation filter is connected as an input to the summingnetwork 40 via a line 106.

To simulate ambient and own ship noise, a range compensation network 108is arranged for connection to source of ambient and own ship noiseindicated and its output is passed on lines 110, I12 and 114 torespective summing networks 82 and 88. The range compensation network108 is designed to have a frequency response corresponding to that ofthe receiver of the particular CTFM sonar being simulated.

Target noise is simulated by providing a second azimuth attenuator 116connected to receive an input from a target noise source indicated andfrom the azimuth function generator 14 via lines 24, 31 and 120 and toprovide an output to the range compensation network 108 via a line 118.

To provide audio as well as visual indication of display signal, anaudio system including a summing network 122, gain control 124,loudspeaker amplifier I26 and loudspeaker 128, is provided. Inputsignals for the summing network are obtained from the band-pass filterchannels via lines 130 and 132 and passed from the summing circuit 122through the gain control 124, loudspeaker amplifier 126 and a line 134to the loudspeaker 128. 7

Referring to FIG. 3, there is shown in block diagram one suitablecircuit for a lost time function generator. In FIG. 3, the incomingrange sawtooth signal indicated is received on line 76 from the rangetime base device 78 shown in FIG. 1 and is passed through a capacitivecoupling 136 and thence on lines 138, 140, 142, 144, 146 and 148, aspulses, indicated, to set respective flip-flops 150, 152 and 154 in ON"condition. Flip-flops I50, 152 and 154 are reset to OFF" condition froma counter 156 via lines 158, 160, 162 and 163. Flip-flop 154 provides anON" signal pulse via line 164 to an oscillator 166 which provides timesignals to the counter 156 via line 168, a divider 170 and a line 172.The counter is connected internally so that each time a pulse is appliedto its input a logical one shifts from one output connection to the nexthigher connection. The counter 156 and the divider 170 are actuated toreset position when the one" reaches the upper or last output via lines174, 176 and 178. The output of flip-flops 150 and 152 provides theinput signals for the respective lost time gates 70 and 68 via lines 72and 71 (see FIG. 1). A resistor 180 (see FIG. 3) is connected via lines182 and 184 to ground indicated to provide with capacitor 136 adifferentiating network.

FIG. 4 indicates by curves the operation of the lost time" functiongenerator of FIG. 3. Curve a indicates the range sawtooth signal comingin on line 76. This signal (see FIG. 3) is converted to a series 'ofpulses, indicated on line 142, to activate flip-flops I50, 152 and 154to ON" condition. Curve b indicates the ON" condition of flip-flop 154.Curve indicates the counter sequential output pulses. Curve d indicatesthe OFF" condition of flip-flop 152 and curve e indicates the OFFcondition of flip-flop 150. Flip-flops 150 and 152 in turn hold losttime gates 70 and 68 in OFF condition by output signals on lines 72 and71.

From FIG. 3 it is apparent that the complete lost time" cycle can becontrolled by proper choice of frequencyf of the oscillator 166. Oncef,, is properly related to the lost time on a particular range scale,then if the scale is halved f would have to be doubled, and so on forother relations.

FIG. is one suitable arrangement for the azimuth function generatorshown in block form at 14 in FIG. 1. As shown in FIG. 5, a reversiblemotor 186 having a motor reversing circuit 188 connected thereto bylines 190 and 192 is provided to drive a potentiometer 194 having an arm196. The voltage from the potentiometer arm 196 is triangular inwaveform and is used to deflect the CRT beam horizontally and is alsocompared with computer generated azimuth reference voltages to generateazimuth gates. Thus, the potentiometer arm is connected via lines 198,200 and 202 as inputs of azimuth comparators 204 and 206. The referencevoltage applied to azimuth comparator 206 is derived via lines 208 and210 from a digital to analog D/A converter 212 which changes a digitalnumber corresponding to an azimuth command (the target appears at thisazimuth) to a direct current voltage. The azimuth command is receivedfrom the problem computer of FIG. 1 via line 12. The same voltageattenuated by resistance networks 214 and 216 and connected by lines218, 220 and 222, is used also as the reference for azimuth comparator204.

Azimuth comparators 204 and 206 are connected through gates 224, 226,228 and 230 as indicated to a normally OFF flip-flop 232. Thus, azimuthcomparator 204 is connected to gates 224 and 228 via lines 234, 236 and238. Azimuth comparator 206 is connected to gates 226 and 230 throughlines 240, 242 and 244. Gates 226 and 228 are connected to flipflop 232via lines 246, 248 and 250 and gates 224 and 230 are connected toflip-flop 232 via lines 252, 254 and 256. The output of flip-flop 232 isconnected via lines 24, 31, 27 to the gate 29 of FIG. 1. A high-limitcomparator 258 and low-limit comparator 260 are connected to a flip-flop264 via respective lines 266 and 268, and are actuated from the voltageof the potentiometer arm 196 via lines 270, 272 and 274. The output offlip-flop 264 is used to actuate the gates 224 and 226 via lines 276,278, 280 and 282 and to operate the gates 228 and 230 via lines 284,286, 288 and 290. The output of flip-flop 264 is also used to operatethe motor reversing circuit 188 via lines 276, 292, 284 and 294.

To describe the operation of the azimuth function generator of FIG. 5,assume that the voltage across the potentiometer arm 196 is initiallylower than the trigger level of comparators 204 and 206 and that itbegins to increase. As the voltage crosses the reference level ofcomparator 206 the comparator generates a pulse that is applied throughgate 226 to the set input of flip-flop 232 (assumed to have been in OFF"condition previously). A logic one appears at the output of flipflop 232and turns on the gate 29 of the programmable oscillator 18 of FIG. 1. Asthe voltage continues to increase it crosses the reference of azimuthcomparator 204. The resultant trigger pulse is applied through gate 224to the reset input of flip-flop 232, turning it OFF" and hence closingthe gate 29 of the programmable oscillator 18. As the potentiometer 194continues to rotate the voltage across its arm 196 rises to some maximumvalue. At this point (or for any greater voltage) the high-limitcomparator 258 triggers, applying a signal to the reset terminal R offlip-flop 264, changing its output to zero and hence closing gates 224and 226. This action also causes the polarity of the voltage applied tothe motor 186 to reverse via the motor reversing circuit 188 making themotor rotate in the opposite direction. The voltage across thepotentiometer arm then begins to decrease. When the voltage reaches apredetermined lower point azimuth comparator 204 triggers and throughgate 228 applies a pulse to the set input S of flipflop 232. This turnson the programmable oscillator 18, FIG. 1, via gate 29 as before. Whenthe potentiometer arm voltage reaches a still lower point azimuthcomparator 206 operates, applying a pulse through gate 230 to the resetof flip-flop 232 shutting off the oscillator 18 via gate 29. As thepotentiometer rotation continues the voltage across its arm reaches avalue below which the low-limit comparator 260 triggers and applies asignal to the set input of flip-flop 232. This causes a one" to appearat its output which reverses the direction of the motor and opens gates224 and 226. Gates 228 and 230 are closed. The cycle is then repeated.

A manually operated reset circuit 296 comprising a resistor 298, acapacitor 300 and switch 302 are connected as shown to a source ofpositive voltage indicated and by line 304 to the reset R of flip-flop232, is provided to reset flip-flop 232 to OFF condition if by chance itstarts in the ON" condition when power is first applied.

Usually there would be more than one target, or a given target mayconsist of a number of distinct highlights so that the computer 10 mustbe able to handle this problem In addition, use of more than oneprogrammable oscillator will be necessary whenever the problem resultsin more than one target within a given bearing sector.

FIG. 6 shows a suitable circuit for the azimuth attenuators 26 and 116of FIG. I. In the azimuth attenuator of FIG. 6, the azimuth gate signalfrom the azimuth function generator 14 turns on a gate 306 connected bylines 308 and 310 to a clock 312 and to a pulse generator 314 and thencevia line 316 to a counter (or shift register arrangement) 318. Counter318, through terminals a, b, c, d, e and lines 320, 322, 324, 326 and328, is connected to the respective gates of field effect transistors(FETs) 330, 332, 334, 336 and 338. The FETs (source-drain) are connectedrespectively by lines 340, 342, 344, 346 and 348 through respectiveresistors 352, 354, 356, 358 and 360 to a common line 362 connectedthrough a resistor 364 to ground indicated. When gate 306 is turned on.the clock 312 applies a signal to pulse generator 314 whose outputactuates counter 318. Successive pulses cause output signals to appearsequentially at terminals :1 through c and turn on the FETs 330, 332,334, 336 and 338 sequentially allowing, dependent upon the selectedvalues of resistors 350 to 358, smaller or larger signals from theprogrammed oscillator 18 to appear across the output resistor 364 of theazimuth attenuator. The attenuated signal from the azimuth attenuator istaken on a line 366 to the associated summing network of FIG. 1. It isevident that as many steps as desired may be employed to approximate anydesired target-beam response curve.

Operation Assume that a fixed, point target is at a range R and azimuth6 relative to the sonar. Under these conditions each time the receivinghydrophone scans past the target an echo of frequency f=(2R/C)(df/dt)will be heard on the loudspeaker and displayed on the CRT, where C isthe velocity of sound in water and dfldt=k is the rate in cycles persecond at which the transmitted frequency is being changed (see FIG. 2).Thus, if 2R/C=l second and df/dr=l,000 cycles per second per second, f=ll ,000=l ,000 cycles/sec. A target twice as distant would return an echoof 2,000 cycles per second; one-half as far would return an echo of 500cycles/sec. The range scale is changed by increasing or decreasing af/dtso that a given frequency does not correspond to a single range.

if relative motion exists between the sonar platform and the target theecho frequency where R is the range rate in knots between the sonar andthe target and f, is the mean transmitted frequency. If the target isstationary where Y is the velocity of the sonar platform in knots and 6is the angle between the velocity vector and the direction to thetarget.

The duration of the echo (assuming a point target) is r=lw seconds where48 is the receiving beamwidth and m is the rate at which the hydrophoneis scanned in azimuth. If for example. d =5 and (u is 3.0 per sec., ther=5/30=0. 166 sec.

Referring to the overall block diagram, FIG. 1, to simulate thephenomena discussed above and the phenomena of reverberation, noise andlost time" the programmable oscillator 18 is adjusted to a frequency Fequal to that which would be generated by a moving or stationary targetat range R by means of a signal from the computer 10. The output ofazimuth function generator 14 on line 20 causes the CRT 22 beam to sweepover the scope face corresponding to the changes in direction in whichthe receiving hydrophone (not shown) points. When the direction of thehydrophone (not shown) and the position of the beam agree with theazimuth at which a target is to appear, the programmed oscillator 18 isturned on by the gate 29 signal from azimuth function generator l4.feeding a signal through azimuth attenuator 26, gain adjuster 38 andsumming network 40. The azimuth attenuator changes the level of theoscillator output as the azimuth changes in the same manner as the echowould change when a receiving hydrophone (not shown) scans past thetarget (not shown). The gain adjuster 38 changes the average intensityof the simulated echo and may be adjusted manually or automatically.

The output of the summing network 40 is applied to lost time" gates 68and 70. summing networks 82 and 88 and thence to band-pass filters 42and 48. It is to be noted for simplicity only two band-pass filterchannels have been shown. in a complete system to 50 filters and gateswould be used. Each filter passes a band of frequencies corresponding toa range interval 137 Detectors 44 and 50 rectify the filter outputs. Thedetectors are scanned sequentially by detector sampler 58. Signals ofvertical scan and intensity are supplied from detector sampler 58 to theCRT 22. The detector scanning rate and the CRT vertical deflection rateare synchronized so that a signal (such as the output of the programmedoscillator) that lies within the passband of a given filter will causean intensity modulated spot to appear at the same CRT range eachvertical scan.

One output, line 20, of the azimuth function generator 14 is applied tothe CRT horizontal detection input, causing the beam to move across theface of the tube. Thetarget appears at the ordered azimuth over a sectorcorresponding to the receiving beamwidth. It is assumed for discussionthat a 8" scope display is used.

Also appearing on the face of the CRT 22 will be signals caused by thereverberation noise generator 94, whose output is applied to gainadjuster 100, thence to range attenuation filter 96, to summing network40 and to band-pass filters 42 and 48. The reverberation generator is awide band source and causes random signals to appear on each channelwith an intensity depending upon the adjustment of the gain control andthe reverberation spectrum as determined by range attenuation filter 96.

There are two related factors that will influence the design of thesimulator. First, both desired echoes and reverberation become weakerwith increasing range in a real world situation. Second, in an attemptto compensate for this fact CTFM receivers are designed to have aprogressively greater response with increasing frequency, frequently atthe rate of 9 to 12 db. per octave. For example, the response at 2,000Hz. may be 24 db. greater than at 500 Hz. The compensation is notnecessarily perfect, however. Detected noise is fairly uniform over thissame frequency range so that the effect of the increased high-frequencyamplification is to make the noise appear to be much stronger at thehigher frequencies (longer ranges).

In the circuit of FIG. 1, the effect ofless than perfect reverberationcompensation is introduced by sloping off the reverberation by the rangeattenuation filter 96. That is, it is assumed that the gain of theparticular receiver does not increase rapidly enough with frequency tocompensate for the loss in amplitude of the reverberation at thesefrequencies.

Own ship, ambient and target noise is fed through a range compensationnetwork 108 that raises the high-frequency components at the same rateas is normally accomplished in the receiver. Ambient, own ship andtarget noise is inserted as shown to the summing networks 82 and 88 toprevent it from passing through the lost time" gates. Lost time appliesonly to target echoes and reverberation. The azimuth attenuator 116 isprovided to cause the target noise to change in intensity as thesimulated beam sweeps across the target. The target can be a noisesource other than the one returning the echo if the problem computer isproperly programmed.

in addition to being applied as signal voltages to the ,CRT, thesimulated reverberation noise and signal are applied to summing network19 and gain control 124 to the amplifier loudspeaker combination 126 and128.

Several advantages of the above-described invention are apparent. Thesimulator is designed to be programmable and hence it is compatible withteam training use. The duration of a training session is not limited bythe length of an operational magnetic tape, hence tests of operatorperformance as a function of time can readily be carried out. Operatortraining in video adjustment is enhanced by the azimuth attenuatorfeature. The echo can be made to resemble either a simple point sourceor a multirefiector echo whose apparent length is a function of aspect.A complex echo can be generated by plugging in a number of adjacent,simple echoes. All realistic features of operational equipment includinglost time" phenomena are attainable in simulation.

What is claimed is:

l. A frequency modulation sonar simulator comprising:

computer means for receiving problem variables and providing outputs ofazimuth and range command electrical signals;

a programmable oscillator and azimuth function generator connected toreceive respectively said range and azimuth signals from said computermeans. said oscillator being programmed in frequency by said rangecommand;

a first azimuth attenuator connected to said azimuth function generatorand said oscillator to adjust the oscillator output level as the azimuthchanges;

a first summing network connected to receive the output of said azimuthattenuator;

a cathode-ray tube device for displaying sonar signals;

a plurality of discrete band-pass filter networks, each including aband-pass filter connected to receive the output of said first summingnetwork, each filter being selected to pass a band of frequenciescorresponding to a range interval;

detector means connected to said band-pass filter networks;

a detector sampler circuit connected to sequentially sample saiddetector means and providing intensity and vertical deflection inputs tosaid cathode-ray tube;

said cathode-ray tube being connected to said azimuth function generatorto receive horizontal deflection input to said tube.

2. Apparatus according to claim 1, including a range compensationnetwork for receiving ambient noise and own ship noise electricalsignals and connected to pass output signals to each of said band-passfilter circuits, to simulate on said cathode-ray tube conditions ofambient noise and own ship noise.

3. Apparatus according to claim 2, including a second azimuth attenuatorfor receiving target noise input electrical signals and an input fromsaid azimuth function generator;

said second azimuth attenuator having an output connected to said rangecompensation network to simulate on said cathode-ray tube conditions oftarget noise.

4. Apparatus according to claim 1, including a plurality of lost timegates connected one to each of said band-pass filter circuits;

a range time base signaling means;

a lost time function generator connected to said range time base and toeach of said lost time gates to pass an electrical signal input to eachof said lost time gates;

said lost time gates being connected to said first summing network toprovide a second electrical signal input to said lost time gates toprovide on said cathode-ray tube an interruption of signal representinglost time phenomena.

5. Apparatus according to claim 1, including a range time base, a rangeattenuation filter and a reverberation generator;

said reverberation generator and said range time base being connected toprovide input electrical signals to said range filter;

said range filter having an output connected to said first summingnetwork to provide the effect of reverberation on said cathode-ray tubeand to alter said effect in accordance with the range scale used.

1. A frequency modulation sonar simulator comprising: computer means forreceiving problem variables and providing outputs of azimuth and rangecommand electrical signals; a programmable oscillator and azimuthfunction generator connected to receive respectively said range andazimuth signals from said computer means, said oscillator beingprogrammed in frequency by said range command; a first azimuthattenuator connected to said azimuth function generator and saidoscillator to adjust the oscillator output level as the azimuth changes;a first summing network connected to receive the output of said azimuthattenuator; a cathode-ray tube device for displaying sonar signals; aplurality of discrete band-pass filter networks, each including aband-pass filter connected to receive the output of said first summingnetwork, each filter being selected to pass a band of frequenciescorresponding to a range interval; detector means connected to saidband-pass filter networks; a detector sampler circuit connected tosequentially sample said detector means and providing intensity andvertical deflection inputs to said cathode-ray tube; said cathode-raytube being connected to said azimuth function generator to receivehorizontal deflection input to said tube.
 2. Apparatus according toclaim 1, including a range compensation network for receiving ambientnoise and own ship noise electrical signals and connected to pass outputsignals to each of said band-pass filter circuits, to simulate on saidcathode-ray tube conditions of ambient noise and own ship noise. 3.Apparatus according to claim 2, including a second azimuth attenuatorfor receiving target noise input electrical signals and an input fromsaid azimuth function generator; said second azimuth attenuator havingan output connected to said range compensation network to simulate onsaid cathode-ray tube conditions of target noise.
 4. Apparatus accordingto claim 1, including a plurality of lost time gates connected one toeach of said band-pass filter circuits; a range Time base signalingmeans; a lost time function generator connected to said range time baseand to each of said lost time gates to pass an electrical signal inputto each of said lost time gates; said lost time gates being connected tosaid first summing network to provide a second electrical signal inputto said lost time gates to provide on said cathode-ray tube aninterruption of signal representing lost time phenomena.
 5. Apparatusaccording to claim 1, including a range time base, a range attenuationfilter and a reverberation generator; said reverberation generator andsaid range time base being connected to provide input electrical signalsto said range filter; said range filter having an output connected tosaid first summing network to provide the effect of reverberation onsaid cathode-ray tube and to alter said effect in accordance with therange scale used.